Groundwater arsenic in the Red River delta, Vietnam ... - Fiva

More documents

Recommendations

Info

Jessen et al., manuscript to be submitted to Geochim. Cosmochim. Acta hematite (ferrihydrite was not identified). The sediment showed an increased release of As in incubations amended with acetate, compared to unamended incibations (Postma et al., submitted), suggesting an association of As with a reducible phase such as an iron oxides. Others have emphasized that biotite and muscovite may be important adsorbents for As in Holocene aquifers (Dowling et al., 2002; Chakraborty et al., 2007; Seddique et al., 2008). Polizzotto et al. (2006), using EXAFS and XANES, did not identify iron (hydr)oxides in their Holocene aquifer sediment. Previously, As has been assumed to be adsorbed to mixed-valence iron minerals (Harvey et al., 2002; Swartz et al., 2004), based on the high solid Fe(II)/Fe(III) ratios of >0.9 observed by Fe(II)/Fe(III) speciation by Mössbauer spectroscopy (Norrman et al., 2008) and in HCl extracts of reduced Holocene sediments of the southeast Asian deltas (Horneman et al., 2004; van Geen et al., 2008). In summary the precise phases to which As(III) is associated in the natural sediments is highly uncertain and presumably varies depending on the sediment. 4.2. Field experiment: flow regime and controlling chemical reactions The forced gradient experiment was conducted to investigate the in situ mobility of As, by pumping low-As river water into the reduced aquifer. The EC in Fig. 6a indicates that after ~17 days of pumping, channel water reaches N1, and five days later, N4. After the flow reversal, the EC first increases in N4 and then in N1. Hence, the data points from N1 envelopes the data points from N4. This symmetry around the time of the reverse in flow direction (day 34) is observed for all the major solutes, and is consistent with a complete breakthrough of water with a constant EC in N1 and a delayed near- complete breakthrough in N4. 21
Jessen et al., manuscript to be submitted to Geochim. Cosmochim. Acta The isotope data (Fig. 9), however, show that the water sampled in the well field during pumping is different from the water sampled in the channel, as reflected by the deviation between the 18 O-value of the groundwater and the 18 O-value of the channel water on day 34. The 18 O-values in N1 and N4 at day 34 are higher, relative to that of the channel, because of 18 O-enrichment of the channel water during the dry season, when the channel is not connected to the Red River (Larsen et al., 2008). The water drawn to N1 and N4 during pumping must therefore be channel water that has infiltrated through the channel bottom during the dry season. A simple PHREEQC transport model was constructed to simulate conservative mixing during transport between the initial groundwater and infiltrated channel water with a composition corresponding to that observed around day 34 in N1. The model consisted of a one-dimensional flow-tube with 32 cells, each 3.3 m long. The observation well N1 was represented by cell 20 and N4 by cell 25, and the corresponding location of the pumping wells were at cell 32. Using the forward- backward flow direction option in PHREEQC, for the initial 34 shifts a forward flow was applied, directly followed by 20 shifts of backward flow. Applying a time step of 1 day per shift during the first 34 days, this set-up yielded the observed five days travel time and a 16 m distance between the two observation wells. After day 34 a longer time step of 1.3 days was applied, corresponding to a decrease in the flow velocity. By optimization for the major solutes, a dispersivity of 2.3 m was achieved. This dispersivity value is within the range typically observed for flow lengths of 10 1 -10 2 m (Gelhar et al., 1992). The match between the observations and the model lines for N1 and N4 in Figs. 6, 7 and 8 indicates that the above described flow regime control the major chemistry variation of the groundwater during the experiment. 22
Page 1 and 2:
Groundwater arsenic in the Red Rive
Page 3 and 4:
Søren Jessen Groundwater arsenic i
Page 5 and 6:
organic matter may prevent As mobil
Page 8 and 9:
Resumé Naturligt frigivet arsen (A
Page 10 and 11:
efterfølgende forsøgt at opstille
Page 12 and 13:
Preface This PhD thesis deals with
Page 14:
Table of contents 1 INTRODUCTION: T
Page 17 and 18:
The PhD research presented in this
Page 19 and 20:
educed form as As(III), which is al
Page 21 and 22:
A more complex and intimate relatio
Page 23 and 24:
sedimentary As content (Postma et a
Page 25 and 26:
(Anawar and Mihaljevi, 2009), and g
Page 28 and 29:
3 Regional As distribution in the R
Page 30 and 31:
in large part by changes in the eus
Page 32:
In the Red River delta, the Pleisto
Page 35 and 36:
the Red River delta, which are not
Page 38 and 39:
5 The mitigation potential of bank
Page 40:
Noteworthy is, that the ratio of Fe
Page 43 and 44:
trend in the distribution of the RF
Page 45 and 46:
2008) or the Hach or Merck test kit
Page 47 and 48:
Badloe C., Nguyen T. P. T. and Nguy
Page 49 and 50:
Driehaus W., Seith R. and Jekel M.
Page 51 and 52:
Islam F. S., Boothman C., Gault A.
Page 53 and 54:
Mondal D. and Polya D. A. (2008) Ri
Page 55 and 56:
A. Ali and Z. Adeel). ITN Centre, B
Page 57 and 58:
Ahmed K. M. (2006) A transect of gr
Page 60:
Arsenic in groundwater of the Red R
Page 63 and 64:
In short, there is a consensus amon
Page 65 and 66:
The local geology shows mainly sand
Page 67 and 68:
ane concentration and P CO2 values
Page 69 and 70:
Fig. 7. The distribution of arsenic
Page 71 and 72:
H3AsO3 þ H2O $ H2AsO4 þ 3H þ þ
Page 73 and 74:
Fig. 12. The relative composition o
Page 75 and 76:
of the Fe-oxides in the upper 3 m c
Page 77 and 78:
found that while As(V) coprecipitat
Page 79 and 80:
desh: further evidence of decouplin
Page 82 and 83:
Controlling geological and hydrogeo
Page 84 and 85:
Here the results of the geological
Page 86 and 87:
sediments. In general, the coarser
Page 88 and 89:
Fig. 5. Thickness of the clay-rich
Page 90 and 91:
a b c The groundwater head distribu
Page 92 and 93:
Table 2 Total As and stable isotope
Page 94 and 95:
delayed yield from the fine grained
Page 96 and 97:
that the situation in Dan Phuong co
Page 98:
Mathers, S., Zalasiewicz, J., 1999.
Page 102 and 103:
0883-2927/$ - see front matter © 2
Page 104 and 105:
3118 S. Jes sen et al. / Applied Ge
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112:
Page 116 and 117:
Postma et al., submitted to Geochim
Page 118 and 119:
Page 120 and 121:
Page 122 and 123:
Page 124 and 125:
Page 126 and 127:
Page 128 and 129:
Page 130 and 131:
Page 132 and 133:
Page 134 and 135: Postma et al., submitted to Geochim
Page 162: The mobility of arsenic in a Red Ri
Page 165 and 166: Jessen et al., manuscript to be sub
Page 183: Jessen et al., manuscript to be sub
Page 207 and 208: Table 1
Page 209 and 210: Fig. 1
show all

Groundwater arsenic in the Red River delta, Vietnam ... - Fiva

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?